﻿using System;
using System.Text;

namespace DPE.Core.Common.Helper;

public sealed class Base32Helper
{

    // the valid chars for the encoding
    private static string ValidChars = "QAZ2WSX3" + "EDC4RFV5" + "TGB6YHN7" + "UJM8K9LP";

    /// <summary>
    /// Converts an array of bytes to a Base32-k string.
    /// </summary>
    public static string ToString(byte[] bytes)
    {
        StringBuilder sb = new StringBuilder();         // holds the base32 chars
        byte index;
        int hi = 5;
        int currentByte = 0;

        while (currentByte < bytes.Length)
        {
            // do we need to use the next byte?
            if (hi > 8)
            {
                // get the last piece from the current byte, shift it to the right
                // and increment the byte counter
                index = (byte)(bytes[currentByte++] >> (hi - 5));
                if (currentByte != bytes.Length)
                {
                    // if we are not at the end, get the first piece from
                    // the next byte, clear it and shift it to the left
                    index = (byte)(((byte)(bytes[currentByte] << (16 - hi)) >> 3) | index);
                }

                hi -= 3;
            }
            else if (hi == 8)
            {
                index = (byte)(bytes[currentByte++] >> 3);
                hi -= 3;
            }
            else
            {

                // simply get the stuff from the current byte
                index = (byte)((byte)(bytes[currentByte] << (8 - hi)) >> 3);
                hi += 5;
            }

            sb.Append(ValidChars[index]);
        }

        return sb.ToString();
    }


    /// <summary>
    /// Converts a Base32-k string into an array of bytes.
    /// </summary>
    /// <exception cref="System.ArgumentException">
    /// Input string <paramref name="s">s</paramref> contains invalid Base32-k characters.
    /// </exception>
    public static byte[] FromBase32String(string str)
    {
        int numBytes = str.Length * 5 / 8;
        byte[] bytes = new Byte[numBytes];

        // all UPPERCASE chars
        str = str.ToUpper();

        int bit_buffer;
        int currentCharIndex;
        int bits_in_buffer;

        if (str.Length < 3)
        {
            bytes[0] = (byte)(ValidChars.IndexOf(str[0]) | ValidChars.IndexOf(str[1]) << 5);
            return bytes;
        }

        bit_buffer = (ValidChars.IndexOf(str[0]) | ValidChars.IndexOf(str[1]) << 5);
        bits_in_buffer = 10;
        currentCharIndex = 2;
        for (int i = 0; i < bytes.Length; i++)
        {
            bytes[i] = (byte)bit_buffer;
            bit_buffer >>= 8;
            bits_in_buffer -= 8;
            while (bits_in_buffer < 8 && currentCharIndex < str.Length)
            {
                bit_buffer |= ValidChars.IndexOf(str[currentCharIndex++]) << bits_in_buffer;
                bits_in_buffer += 5;
            }
        }

        return bytes;
    }
}
